In order to avoid erroneous detection due to electric noise, a conventional obstacle detection device determines whether it has continuously detected that an obstacle is existing at the same position (in the same direction and at the same distance) twice, and, when having continuously detected that an obstacle is existing at the same position twice, recognizes that there is an obstacle.
For example, according to a related art technique described in patent reference 1, a continuous transmission of an ultrasonic pulse is carried out, and, when a reflection signal having the same pulse width has been continuously detected, it is recognized that the reflection signal has come from an obstacle.
Further, according to a related art technique described in patent reference 2, because a simultaneous transmission of ultrasonic pulses from a plurality of ultrasonic sensors causes interference between transmission waves and hence an undetectable area, any two adjacent ultrasonic sensors which transmit transmission waves which may interfere with each other are prevented from transmitting transmission waves simultaneously.